1. Field of the Invention
The present invention relates to synchronizing the voltage of position sensors, and more particularly to a method for synchronizing the zero position of a plurality of pedal position sensors in the automotive industry.
2. Background of the Invention
Position sensors are used to allow an electrical circuit to gain information about an event or a continuously varying condition. A type of position sensor is a potentiometric sensor. Potentiometric sensors are widely used as position sensors in various automotive applications. In particular, potentiometric sensors are used to obtain throttle and accelerator pedal position measurements.
With the introduction of electronically controlled engines, electronically controlled transmissions and electronic throttle control devices, a rotary potentiometer sensor is one type of sensor used for detecting the angular position or movement of the accelerator pedal.
Potentiometric sensors are used as voltage dividers, A voltage is applied across two extreme ends of a resistor. An intermediate tap is provided between the two extremes of the resistor. The tap is mechanically linked to the device which is to be sensed, and the position of the device is determined by the voltage at the intermediate tap.
The accelerator pedal position sensors detect the actual accelerator pedal position and outputs an accelerator pedal position signal to the electronic engine control unit (ECU) and the electronic automatic transmission controller (EATX), respectively. The ECU determines a target throttle position in response to the actual accelerator pedal position and other parameters representing engine driving conditions. The EATX translates the actual accelerator pedal position into the throttle angle in a similar way as the ECU does.
When an accelerator pedal position is requested by the driver, the ECU calculates the target throttle according to the request and sends the throttle related information to the EATX.
A common problem when applications include a plurality of sensors (pedal position sensors) is that the voltage may vary from sensor (pedal position sensor) to sensor (pedal position sensor) due to production variation even for a fixed pedal position. In the intended application, absence of synchronizing the zero position of the pedal position sensors, the EATX and the ECU would interpret a pedal angle request differently, thus the performance of the vehicle is hindered.
Therefore, this invention provides a more accurate and reliable method of ensuring that each automotive electronic controller is obtaining synchronized interpretation, or establishing a common reference point of the voltage from the pedal position sensors at any given pedal position.
The present invention overcomes the aforementioned disadvantages as well as other disadvantages. In accordance with the teachings of the present invention, the present invention provides a more accurate and reliable method of ensuring that the automotive electronic controllers are obtaining synchronized interpretation of the voltages when a plurality of pedal position sensors are present.
In a vehicle with Electronic Throttle Control (ETC), the accelerator pedal controls pedal position sensors (PPS) and according to the voltage from the PPS, the ECU controls the throttle opening. In a vehicle with an Engine control unit (ECU) and an Automatic Transmission Controller (EATX), the EATX and ECU may have independent PPS responding to the accelerator pedal. The voltage for a same pedal position may vary from PPS to PPS due to production variation, and the controllers may obtain different pedal positions from their own PPS. This hinders the performance of the vehicle.
In the present application, the ECU uses a predefined threshold that does not change with different PPS. The EATX also uses a threshold. In order to compensate for PPS production variations, a method has been developed to adapt the EATX threshold to achieve synchronization with the ECU threshold. Since in this application the ECU and EATX are separate modules and they communicate through a communication BUS with significant latency, this method also identifies the ECU and EATX PPS voltage readings (or their interpretations) that correspond to the same steady pedal positions.
It is an object of the invention to provide a method which is capable of synchronizing a plurality of pedal position sensors, providing the equal pedal angle information to the automotive electronic controllers regardless of the rotation angle of the pedal.
The ECU reads its PPS voltage (PPS1) and compares it against a threshold. When the voltage is below the threshold, the ECU assumes a zero pedal requested throttle. The ECU computes a throttle opening from the difference between the voltage and the threshold when the read voltage is above the threshold. The ECU then controls the ETC to achieve the desired throttle and controls the engine accordingly.
The EATX reads a voltage from a different PPS (PPS3) and compares it against its threshold. When this voltage is below the threshold, the EATX assumes a zero throttle. The EATX also computes a throttle from the difference between the voltage and the threshold when the voltage is above the threshold.
To best control the transmission, the EATX needs to be synchronized with the ECU on PPS voltage interpretation, or in other words, the threshold voltages of the EATX and ECU should correspond to the same pedal position. Then, the EATX and ECU will both interpret a zero or non-zero throttle from the same pedal position.